Process for preparing a diamine/dicarboxylic acid salt

ABSTRACT

The present invention also relates to a process for preparing a diamine/dicarboxylic acid salt wherein the dicarboxylic acid comprises an aromatic dicarboxylic acid and is provided in a powder form; the diamine is provided in a liquid form gradually dosed to the dicarboxylic acid powder, while keeping the dicarboxylic acid powder in constant movement; the processing temperature is above 0° C. and below the boiling temperature of the diamine and the melting temperature of the acid and the salt, and the reaction mixture comprises at most 5 wt. % of water. The present invention also relates to an anhydrous diamine/dicarboxylic acid salt obtainable by the process according to invention, or any embodiment thereof as described above.

This application is a continuation of U.S. application Ser. No.14/234,248, filed Apr. 18, 2014 (now U.S. Pat. No. 9,475,753), which isthe national phase application of international applicationPCT/EP2012/064698, filed Jul. 26, 2012, which designated the US andclaims priority to European Application No. 11175378.6, filed Jul. 26,2011, the entire contents of each of which are hereby incorporated byreference.

The present invention relates to a process for preparing adiamine/dicarboxylic acid salt comprising contacting a diamine with adicarboxylic acid to provide a reaction mixture in which said diamineand said dicarboxylic acid react to form a diamine/dicarboxylic acidsalt.

Diamine/dicarboxylic acid salts are widely used as starting materialsfor the production of polyamides. Particularly favourable, thediamine/dicarboxylic acid salt has a solid particulate form.

Poly(hexamethylene adipamide) (nylon 6,6) polymer is typicallymanufactured commercially by first making an aqueous salt solution fromits monomers hexamethylene diamine and adipic acid. The diamine issupplied as a dilute aqueous solution so that the resultinghexamethylene diammonium adipate (6,6 salt, often referred to as nylon6,6 salt) solution usually contains about 50 wt. % water. This solutionis then used as a starting material and initial reaction medium for thesolution/melt polymerization of nylon 6,6. Sometimes also aqueoussolutions of nylon 6,6 salt are sold commercially, which are typicallytransported as warm solutions of about 50 wt. %. Storing times arelimited due to the unwanted polymerization and warm storage of thesolutions is required to avoid precipitation of the sold in the storagevessel. Nylon 6,6 salt is also commercially available as a solid.Techniques are known for precipitating the salt from the solution suchas by adding a non-solvent for the salt to the solution, e.g.,isopropanol. Such processes require the subsequent recovery of thenon-solvent from the solution. The salt can be recovered as a stable,free-flowing powder which is easily shipped for use at remote locations.This is less dangerous than shipping caustic volatile hazardous aqueoussolutions of hexamethylene diamine, which solution is a typical form forshipping the diamine to keep it in the liquid state at moderatetemperatures.

An alternative process to produce diamine/dicarboxylic acid salts insubstantially solid particulate form is known from U.S. Pat. No.5,801,278. In the process from U.S. Pat. No. 5,801,278 the reaction ofthe diamine with a dicarboxylic acid is carried out in the presence ofabout 0.5 to about 25 wt. % water, preferably 2-10 wt. % water, based onthe weight of the reaction mixture, while providing conditions in thereaction mixture such that the reaction mixture is in substantiallysolid particulate form. These conditions were met by employing atemperature well below room temperature, more particularly using acryogenic medium, such as dry ice or liquid nitrogen, in the reactionmixture. The reactants were mixed in a short time and subsequentlykneaded for allowing the reactants to react. Where the reaction wasperformed without a cryogenic medium, it resulted in formation of apaste rather than a free flowing powder. Also the homogeneity of theresulting product was not good.

In U.S. Pat. No. 5,874,520 anhydrous nylon salts are made in a solidstate process in which solid diamine carbamates are contacted and mixedwith solid dicarboxylic acids. These compounds are in particular mixedunder high shear conditions, which is to reveal “fresh” particlesurfaces having unreacted molecules by frictional rubbing or the like.Cryogenic media (e.g. dry ice or nitrogen) are used, not only to controlthe heat of the reaction, but also to maintain the reaction in the solidstate.

In U.S. Pat. No. 5,874,520 substantially anhydrous nylon salts are madein a solid state process in which solid diamine carbamates are contactedand mixed with solid dicarboxylic acids in a near instantaneous reactionto produce the salt under conditions of high shear. As mentioned in U.S.Pat. No. 5,874,520 the reaction can be continued by removing the saltformed at the particle-particle interface (such as by frictional rubbingor the like) to reveal “fresh” particle surfaces having unreactedmolecules.

Use of an organic solvent or a cryogenic medium in the way as describedabove complicates the process and is often not desired or even prohibitslarge scale production. A special disadvantage of using cryogenic mediais that they may allow moisture to be drawn from the ambient air, whichin turn may decompose some of the carbamate salt, as mentioned in U.S.Pat. No. 5,874,520, but also may prevent the salt to be recovered fromthe process as a stable, free flowing powder. The use of chemicals likedry ice (CO2) and/or nitrogen, which are subsequently emitted to thesurrounding involves extra costs, and is environmentally unfavourabledue to the carbon footprint of the nitrogen and CO2 used.

The aim of the invention is to provide a process for preparing adiamine/dicarboxylic acid salt, which eliminates the need for using anorganic solvent or a cryogenic medium. The aim is further to provide aprocess wherein the diamine/dicarboxylic acid salt is produced in solidparticulate from, preferably as a free flowing powder.

This aim has been achieved by the process according to the invention,comprising steps comprising contacting a diamine with a dicarboxylicacid to provide a reaction mixture in which said diamine and saiddicarboxylic acid react to form a diamine/dicarboxylic acid salt,wherein:

-   -   (a) the dicarboxylic acid comprises an aromatic dicarboxylic        acid;    -   (b) the dicarboxylic acid is provided in a powder form;    -   (c) the diamine is provided in a liquid form;    -   (d) the contacting is performed by gradually dosing diamine        liquid to dicarboxylic acid powder, while keeping the        dicarboxylic acid powder in constant movement;    -   (e) the reaction mixture is kept in constant movement for a time        period directly following completion of the dosing,    -   (f) (d) and (e) are carried out at a temperature above 0° C. and        below all of the following: the boiling temperature of the        diamine and the melting temperatures of the dicarboxylic acid,        the diamine/dicarboxylic acid salt and any intermediate reaction        product, and    -   (g) in (d) and (e) the reaction mixture comprises at most 5 wt.        % of water, relative to the total weight of the diamine and        dicarboxylic acid.

The effect of the process according to the invention is that the salt isobtained in solid particulate form being substantially anhydrous. By“substantially anhydrous” is meant herein that the salt generallycontains no more than 5 wt. % of water, relative to the total weight.The salt is recovered from the process is a stable, substantially freeflowing powder. The salt is obtained as a generally homogenous product,suitable for use in common commercial processes for the manufacture ofpolyamide polymers. This result is achieved without a precipitation stepinvolving using an organic solvent and without the use of a cryogenicmedium in the reaction mixture. The process does not require high shearmixing, and the process can easily be scaled up to industrial scale.

The temperature at which (d) and (e) are carried out is herein alsoreferred to as processing temperature. This temperature is measured inthe reaction mixture.

With the term melting temperature (Tm) is herein understood thetemperature, measured by the DSC method according to ISO-11357-3.2,2009, in a nitrogen atmosphere with heating and cooling rate of 20°C./min. Herein Tm is the temperature at the peak of the melting peak inthe first heating cycle.

With the term boiling temperature for the diamine is herein understoodthe boiling temperature measured at the prevailing pressure when dosingof the diamine. In a preferred embodiment (d) and (e) are carried out ata temperature below the boiling temperature of the diamine measured atthe lowest pressure applied during the dosing of the diamine.

With the expression “gradually dosing” is herein understood that thediamine is dosed at sufficiently low amount per time unit as to notexcessively wet the particles at any time to prevent sticking of theparticles together, clogging and lump formation. This excludes thediamine to be dosed all at once or nearly so. However, it does notexclude the diamine to be dosed in reasonably short time, as it appearedthat reaction of added diamine with the dicarboxylic acid is reasonablyfast thus preventing the diamine to be accumulated in unreacted form.The reaction speed might depend on the type of diamine and dicarboxylicacid. The dosing regime suitable to be applied in, for example largescale operations for specific combinations of diamine and dicarboxylicacid can be established by routine measurements by simply varying thedosing speed, e.g. starting with a low dosing speed, and graduallyincreasing the speed.

The minimum duration of the time period directly following completion ofthe dosing, during which the reaction mixture is kept in constantmovement is typically chosen to be at least sufficient to preventsticking and agglomeration upon discharging from the reactor in whichthe process is carried out. This is affected by the various factors,such as dosing speed, reaction temperature and combination of specificdiamines and dicarboxylic acids. Suitably, the time period is in therange starting from and including 10 minutes up to and including 1 hour.The time period may also be longer than 1 hour. Depending on processingconditions, in particular with a very slow dosing speed, in particularwith a very slow dosing speed at the end of the dosing of the diamine,this time period can be much shorter, e.g. between 0 and 10 minutes.

The diamine and the dicarboxylic acid in the reaction mixture can bepresent in a molar ratio varying over a large range, with initially thecarboxylic acid being present in large excess over the diamine. Duringthe dosing of the diamine this excess diminishes and the molar amountsget closer to parity, while if further diamine is added the diaminemight be in excess over the diacid. This is not a problem, since addingsome excess of diamine still results in a stable solid particulatematerial.

However, a large deviation of the molar ratio from parity could be lessdesirable for further processing to produce polyamide polymers, as thiswould require supplementation of diamine in case of excess dicarboxylicacid, whereas in case of excess of diamine this would requiresupplementation of extra dicarboxylic acid and/or, with a larger excessof diamine, lead to excessive loss of volatile amines. Suitably themolar ratio of diamine over dicarboxylic acid (D/DA) is in the range of0.9-1.1. Preferably the D/DA molar ratio is in the range of 0.95-1.05.In practice it is preferred that the diamine is at least at parity, thuswith a D/DA of at least 1.0, or in a slight excess, such as with a D/DAmolar ratio of about 1.005-1.02, corresponding to 0.5 to 2% molar excessof diamine. Therefore, more preferably, the D/DA ratio is in the rangeof in the range of 1.00-1.02. Even with such low excess, or even noexcess at all, i.e with equimolar amine, the reaction goes to completeconversion or essentially so, i.e. a small amount of residualdicarboxylic acid if any is observed, e.g. with wide angle X-raydiffraction (XRD). Of course, with less than equimolar diamine, thepresence of a certain amount of residual dicarboxylic acid cannot beexcluded.

The diamine and the dicarboxylic acid used in the process according tothe invention suitably consist of mixtures of different compounds, i.e.mixtures of different diamines and/or mixtures of different dicarboxylicacids. The mixtures can be chosen such as to provide for the preferredcomposition of the copolyamide polymer, depending on the requiredpolymer properties.

In a particular embodiment, the dicarboxylic acid is a mixture of analiphatic dicarboxylic acid and an aromatic dicarboxylic acid. This hasthe advantage that the salt not only is in a solid particulate form butalso comprises a mixture of dicarboxylic acids as are used in severalsemi-aromatic polyamides produced on commercial scale.

It is noted that the use of the expression “a” or “an”, as used herein,for example in here above “an aliphatic dicarboxylic acid” and “anaromatic dicarboxylic acid” is intended herein to include both singularas well as plural forms, unless expressly noted otherwise.

In general the aliphatic dicarboxylic acid and the aromatic dicarboxylicacid are suitably present in a molar ratio between 90:10 and 10:90,although depending on specific diamine and dicarboxylic acid componentsa ratio of 90:10 or above might be used while still obtaining a solidparticulate material. Preferably the molar ratio is in the range of from80:20 up to and including 20:80.

In a preferred embodiment, the mixture of aliphatic dicarboxylic acidand aromatic dicarboxylic acid is a dry blend of solid particles of thealiphatic dicarboxylic acid and solid particles of the aromaticdicarboxylic acid. It has been observed that though the dicarboxylicacids are not mixed on molecular scale prior to the salt productionprocess, the salt is obtained in a solid particulate form, even when thecorresponding salt of the aliphatic dicarboxylic acid, i.e. without thearomatic dicarboxylic acid, gives difficulties in or prohibits theformation of a solid particulate. The use of a dry blend prevents theneed of any complex premixing step such as dissolving, mixing andprecipitation steps.

In cases where a combination of different dicarboxylic acids are used,different salts can be formed which can be reflected in differentmelting peaks, in particular in case where the different dicarboxylicacids are used in the form of a dry blend. These melting temperaturesshall all be considered when choosing the processing conditions. Theprocessing temperature shall be kept below the melting temperature ofeach.

In a particular embodiment the aliphatic dicarboxylic acid and thearomatic dicarboxylic acid are present in a molar ratio between 10:90and 50:50.

In another particular embodiment, the dicarboxylic acid essentiallyconsists of aromatic dicarboxylic acid, with which is meant that thedicarboxylic acid more particularly consists of 90-100 mole % ofaromatic dicarboxylic acid and 10-0 mole % of aliphatic dicarboxylicacid. Preferably dicarboxylic acid consists of 95-100 mole % aromaticdicarboxylic acid, respectively 5-0 mole % aliphatic dicarboxylic acid.The mole percentages (mole %) mentioned are relative to the total molaramount of aliphatic dicarboxylic acid and aromatic dicarboxylic acid.

The aromatic dicarboxylic acids not only favour the formation of thediamine/dicarboxylic acid salt as a solid particulate material, it alsoreacts readily with the diamine. The salts based on dicarboxylic acidessentially consisting of aromatic dicarboxylic acid are furthermorefavourably used in the production of polyamides in combination with asalt based on aliphatic dicarboxylic acid. Herein the salt based onaliphatic dicarboxylic acid comprises or is, for example, nylon 6,6salt, i.e. the salt of 1,6-hexane diamine and adipic acid. Nylon 6,6salt is produced on very large scale and available worldwide.Combinations of these salts allow the production of polyamides withcompositions varying over a wide spectrum, without the need to have alarge inventory on different salts or mixing in of additional amines oracids.

Examples of suitable aromatic dicarboxylic acids include isophthalicacid, terephthalic acid, 2,6-naphthalene dicarboxylic acid and4,4′-biphenyldicarboxylic acid, which can be used individually as wellas in any combination thereof. Preferably, the aromatic dicarboxylicacid comprises 2,6-naphthalene dicarboxylic acid and/or terephthalicacid. More preferably the aromatic dicarboxylic acid comprisesterephthalic acid in an amount of at least 25 mole %, better at least 50mole %, still better at least 75 mole %, or even consists ofterephthalic acid. Herein the mole % are relative to the total molaramount of aromatic dicarboxylic acid.

The aliphatic dicarboxylic acid in the process according to theinvention may be a non-cyclic, either linear or branched dicarboxylicacid or a cyclic dicarboxylic acid. Suitably the aliphatic dicarboxylicacid is an aliphatic dicarboxylic acid having 4-18 carbon atoms, forexample, 6, 8, 10 or 12 carbon atoms. Suitably the non-cyclicdicarboxylic acid is chosen from the group of 1,6-hexanedioic acid (alsoknown as adipic acid), 1,8-octanedioic acid, 1,9-nonanedioic acid,1,10-decanedioic acid (also known as sebacic acid), 1,11-undecanedioicacid, 1,12-dodecanedioic acid, 1,13-tridecanedioic acid,1,14-tetradecanedioic acid, 1,15-pentadecanedioic acid,1,16-hexadecanedioic acid, 1,17-heptadecanedioic acid and1,18-octadecanedioic acid. A suitable cyclic aliphatic dicarboxylic acidis trans-1,4-cyclohexanedicarboxylic acid.

Preferably, the aliphatic dicarboxylic acid comprises adipic acid orsebacic acid. Adipic acid is most widely used in polyamides. Sebacicacid is available from renewable resources.

In addition, mono-acids, for example benzoic acid, can be added to themixture of acids in any desired quantity, as required for quality of thepolymer product eventually obtained. Usually around 0.5 to 3 mole %(relative to the acids already present) of mono-acids are used inpolymerization processes to control the molecular weight of theresulting polyamide. Suitably, the amount of monocarboxylic acid, ifused at all in the salt preparation process, is in the range of 0.01-5,preferably 0.1-3 mole %, relative to the total molar amount ofdicarboxylic acid.

The diamine in the process according to the invention can be selectedfrom those diamines suitable for use as starting materials for themanufacture of polyamides. These diamines include aliphatic diamines,alicyclic diamines, aromatic diamines and any mixture thereof. Suitablearomatic diamines are, for example, isophenylene diamine andparaphenylene diamine. Suitably, the aliphatic diamines are aliphaticdiamines with 2-18 carbon atoms, which may be either linear or branched,or alicyclic. More preferably the aliphatic diamines have 2-12 carbonatoms per molecule, such as 1,2-ethylene diamine, 1,3-propylene diamine,1,4-butane diamine, 1,5-pentane diamine, 1,6-hexane diamine, 1,8-octanediamine, 1,9-nonane diamine, 1,10-decane diamine, 1,11-undecane diamine,1,12-dodecane diamine, 2-methyl-1,5-pentane diamine and2-methyl-1,8-octane diamine. Examples of suitable alicyclic diamines are1,4-trans-cyclohexane diamine and 1,4-trans-diaminomethylcyclohexane.

Preferred diamines are those most widely used in semi-aromaticpolyamides produced on large scale, which include 1,4-butane diamine,1,6-hexane diamine, and 1,9-nonane diamine.

In case of longer chain diamines, such as with C8-C18 diamines, thereaction is slower and longer dosing time and/or higher reactiontemperatures are needed, compared to shorter chain diamines with 2-7carbon atoms per molecule. Preferably, the C8-C18 diamines are combinedwith a C2-C7 diamine. The amount of the C2-C7 diamine can remainrelatively low, which already having a significant effect on thereaction rate, thus allowing for a shorter dosing time and/or a higherreaction temperature. Suitably, the molar ratio between short chaindiamine and long chain diamine is in the range of 1/99-25/75, moreparticular 2/98-20/80, or even 5/95-15/85. Of course also mixtures witha higher molar amount of short chain diamines are suitable for the saltpreparation process

Preferably, the short chain diamine is a C2-C6 diamine. More preferably,the diamine used in the process according to the invention comprises1,4-butane diamine and/or 1,6-hexane diamine, more preferably 1,4-butanediamine.

As mentioned above the process is carried out at a temperature below theboiling temperature measured at the prevailing pressure when dosing ofthe diamine. Where the diamine used in the process of the invention is amixture of at least two different diamines, the boiling temperature ofthe diamine (TbDiamine) below which the temperature in the process is tobe kept, is the lowest of the boiling temperature of any of the at leasttwo diamines and, in case it occurs, any azeotrope thereof. The boilingtemperature, respectively the boiling temperatures referred to hereinare each the boiling temperature measured at the prevailing pressure atwhich the contacting and reaction are carried out. The purpose thereofis to prevent evaporation of the diamine rather than the diaminecontacting and reacting with the dicarboxylic acid.

In a preferred embodiment process steps (d) and (e) are carried out at atemperature below the boiling temperature of the diamine measured at thelowest pressure applied during the dosing of the diamine. In case of amixture of at least two different diamines, the boiling point of thediamine is the lowest of the boiling temperature of any of the at leasttwo diamines and, in case it occurs, any azeotrope thereof.

In the process according to the invention the diamine and dicarboxylicacid are contacted by gradually dosing the diamine liquid to thedicarboxylic acid powder, while keeping the dicarboxylic acid powder inconstant movement. Preferably the diamine is dosed onto the dicarboxylicacid powder, such that it does not first get into contact with a part ofa side wall of a reactor vessel in which the process is carried out.This in order to prevent sticking onto the side wall and lump formationof dicarboxylic acid powder and salt subsequently formed. Suitably thecontacting is performed by spraying or dripping the diamine onto themoving dicarboxylic acid powder.

The process according to the invention can in principle be carried outin any type of reactor in which powder material can be kept in constantmovement by mechanical agitation. By the mechanical agitation amechanically agitated powder bed is formed. Suitable reactors for theprocess to be carried out in are, for example, a tumble mixer, aploughshare mixer, a planetary screw mixer, also known as Nauta mixer, aconical mixer and a fluidized bed, for example a circulating fluidizedbed reactor. The mixers may also contain a wall heating and/or cooling,as is typical for dryers. In said case the mixers may also be referredas dryer, as in tumble dryer conical dryer and planetary screw drier.

The said mixers are all low shear mixers. Further information on theseand other low shear mixer apparatus can be found in the book “Handbookof Industrial Mixing—Science and Practice” edited by: Paul, Edward L.;Atiemo-Obeng, Victor A.; Kresta, Suzanne M. (Publisher: John Wiley &Sons; 2004; ISBN: 978-0-471-26919-9; Electronic ISBN:978-1-60119-414-5), more particularly in Chapter 15, part 15.4 and15.11.

The fact that the process according to the invention can be carried outwithout applying a high shear and still provide a high degree ofconversion is highly surprising. In fact, the constant movement in step(d) and (e) of the process according to the invention can beaccomplished with low shear agitation avoiding attrition of thedicarboxylic acid powder. With such low shear there is also nosignificant break-up of the salt particles, more particular, the d10 ofthe resulting diamine/dicarboxylic acid salt is at least the same asthat of the starting dicarboxylic acid powder. In fact the attrition canbe so low, or even absent at all, that the particle size distribution ishardly affected, apart from the fact that the size of the dicarboxylicacid powder particles might be even increased during the reaction withthe diamine.

The advantage of such low shear agitation without attrition of thedicarboxylic acid powder, is that amount of fines produced during theprocess is low, and that problems of fouling, dusting, sagging uponstorage, and reduced flowability due to clogging of fines is reduced.

In a preferred embodiment of the process according to invention, thedicarboxylic acid powder used therein comprises a low amount ofparticles with small particle size. Also preferred is a dicarboxylicacid powder having a narrow particle size distribution. The advantagethereof is that also the resulting diamine/dicarboxylic acid salt soproduced also has less small particles, respectively a relative narrowparticle size distribution, and optionally even better flow properties.Suitably, the use of dicarboxylic acid powder with low amount of smallparticles and/or narrow particle size distribution, is combined with lowshear agitation.

Suitably, the dicarboxylic acid powder has a particle size distributionwith a d10 of at least 15 μm and a d90 of at most 1000 μm. Suitably, thedicarboxylic acid powder also has a median particle size (d50) in therange of 40-500 μm. Herein the particle size distribution is measuredwith laser granulometry by the method according to ISO 13320 at 20° C.

Preferably the d10 for the particle size distribution of thedicarboxylic acid powder is in the range of 15-200 μm, more preferablyin the range of 16-160 μm. Preferably, the d90 is in the range of100-1000 μm, more preferably in the range of 150-800 μm. Preferably, thed50 is in the range of 40-400 μm, more preferably in the range of 40-400μm. Also preferably the dicarboxylic acid powder has a particle sizedistribution with a Span, defined by the ratio of (d84-d16)/d50, of atmost 5. The advantage is that also the resulting diamine/dicarboxylicacid salt has a narrower particle size distribution and the flow isfurther improved.

The reaction of the diamine and the dicarboxylic acid is carried outunder conditions such that the reaction mixture is continuously insubstantially solid particulate form, i.e. discrete particles existthroughout the duration of the addition of the diamine and thesubsequent reaction time. The reaction of a diamine with a dicarboxylicacid is strongly exothermic, and local overheating could result in someminor agglomeration. Without any temperature control, the reactionmixture could, depending on the reactants used, form a paste andagglomerate into a single mass, rather than to remain in thesubstantially solid particulate form. However, by applying the processaccording to the invention, wherein the diamine is gradually dosed, andthe reaction mixture is kept in constant movement during the diaminedosing and the further reaction, optionally supported by externaltemperature control measures, the temperature is easily controlled andlocal overheating is minimal if any.

The temperature control for maintaining substantially solid particulateform is suitably achieved when during the gradual addition of thediamine and mechanical agitation of the reaction mixture heat istransferred away from the reaction mixture, such as to keep thetemperature of the reaction mixture, i.e. processing temperature, withinthe temperature range indicated above, i.e. in between 0° C. and eitherthe boiling temperature of the diamine (TbDiamine), the meltingtemperature of said dicarboxylic acid, of the diamine/dicarboxylic acidsalt and of intermediate reaction products in the reaction mixture,whichever is the lowest. This heat transfer is advantageouslyaccomplished by employing a reactor equipped with a heat exchanger. Theheat exchanger can be, for example, an internal heat exchanger, such asbaffles with a cooling medium inside the baffles, and/or an externalheat exchanger, such as a double wall reactor vessel, with a coolingmedium inside the double wall.

The processing temperature suitably is chosen to be below the boilingtemperature of water. Thus, the processing temperature may as well bechosen to be equal to or higher than the boiling temperature of water.If the processing temperature is equal to or higher than the boilingtemperature of water under the prevailing conditions of the process,care has to be taken to either maintain the amount of water in thereaction mixture as low as possible, preferably below 1 wt. %, relativeto the total weight of the reaction mixture, and/or to prevent thepresence of cold spots where water vapour could condense and powderparticles could stick to the wall. This latter can be achieved by usinga reactor with a wall temperature above the boiling temperature ofwater. The processing temperature can still be kept below the upperlimit by applying a sufficiently low dosing speed for the diamine. Byapplying a processing temperature above the boiling temperature ofwater, the diamine/dicarboxylic acid salt in solid particulate form isobtained with even lower water content. Special care might be paid toprevent diamine to be entrained and removed together with the watervapour.

Suitably, the diamine and the dicarboxylic acid are contacted at atemperature between 0° C. and the boiling temperature of water. Hereinthe boiling point is the boiling point as measured for the prevailingpressure at the time of dosing of the diamine. The process is optionallycarried out under atmospheric conditions. The process and dosing maywell be carried out at pressures above and/or below atmosphericpressure. Preferably a slight overpressure is applied, optionallyoperating in an inert atmosphere of nitrogen or argon, for example toavoid intake of air.

A particularly preferred way of carrying out the invention is to exposethe dicarboxylic acid in powder form to a low ambient temperature, i.e.,room temperature, and subsequently add a diamine, optionally containingup to about 2 percent water combined therewith, in liquid (molten) form.Using such amines, some heating might be required to maintain theseamines in liquid form for ease of addition to the reaction mixture.Moreover, the rate of addition of the liquid diamine can be easilycontrolled to match the heat transfer conditions, i.e., the liquidaddition can be adjusted to a sufficiently low rate to prevent theformation of a paste.

Unlike conventional diamine/dicarboxylic acid salt formation processeswhich are carried out in aqueous solutions containing approximately 50wt. % water, the water content of the reaction mixture in the process ofthe invention is at a much lower level, that is, at most 5 wt. %,preferably at most 1 wt. % relative to the weight of the reactionmixture. The water content may be even below 0.5 wt. %. Despite the lowwater content, the salt formation reaction occurs to sufficient extentto favour the formation of the salt in sufficiently short time and withreasonable to good homogeneity. With the water content kept within thesaid limits, the diamine/dicarboxylic acid salts are recovered as afree-flowing powder, or substantially so, which facilitate subsequenthandling.

The diamine/dicarboxylic acid salts, which can be stored and shipped insubstantially solid particulate form, are useful starting materials forthe manufacture of polyamide polymers. The salts can be used to makeconventional aqueous solutions containing about 50 wt. % water, for usein known commercial processes for the manufacture of polyamide polymers.

The present invention also relates to a diamine/dicarboxylic acid saltobtainable by the process according to invention, or any embodimentthereof as described above. Preferably, the said according to theinvention is an anhydrous salt, which comprises less than 0.5 wt. %water, relative to the total weight of the salt.

The salt obtained by the process according to the invention is freeflowing, or substantially so. i.e at least easy flowing.

The flowability of powder material can be measured by different methods.A suitable method is the sheartest method according to ASTM D6773. Thistest can be performed with a Schulze Ringshear Tester. In this test theflowability is defined by the ratio (ffc) of consolidation stress, σ1,to unconfined yield strength, σc, For an easy flowing material the ffcshould be above 4, more particular in the range between 4 and 10. For afree flowing material the ffc should be at least 10. According toSchulze a material with an ffc of 4 or less is too cohesive for properflowability.

In the method applied herein further below the flowability was measuredby the sheartest method according to ASTM D6773, with a SchulzeRingshear Tester, with a consolidation stress of 3 kPa, at 20° C., aftera storage time of 10 minutes. The anhydrous diamine/dicarboxylic acidsalt according to the invention has a flowability (ffc) of at more than4, preferably more than 7, and even more preferred above 10.

It has been observed that the diamine/dicarboxylic acid salts obtainedby the process according to invention have a particular morphology,which can be observed by microscopic techniques, more particular byscanning electron microscopy (SEM). The said diamine/dicarboxylic acidsalt is a granulate material consisting of polycrystalline granules, theindividual granules consisting of multiple micro-crystallites and/ormicro-crystalline domains. The micro-crystallites are visible all overthe surface of the granules. The micro-crystallites have a relativelynarrow particle size distribution. The granules consist of suchmicro-crystallites or micro-crystalline domains throughout the granules,as can be observed from SEM pictures taken upon cutting the granules.The average size of the micro-crystallites inside the granules wasobserved to be smaller than of those on the surface.

The micro-crystallites typically have a small particle size, muchsmaller than the granules. Even the smallest granules appear to consistof multiple micro-crystallites.

Suitably, the granules consist of micro-crystallites having a diameterbased particle size distribution, with a d90 of at most 2.5 μm. Thismeans that at least 90% of the total number of micro-crystallites have amean diameter of at most 2.5 μm.

Also suitably, the granules consist of micro-crystallites having avolume based particle size distribution, with a d90 of at most 5 μm.This means that at least 90% of the total volume of themicro-crystallites is made up of micro-crystallites having a meandiameter of at most 5 μm.

Herein the diameter is the mean diameter for individualmicro-crystallites measured by software supported image analysis of SEMimages taken from surface areas of granules, as described herein furtherbelow. The software used is “Analysis.auto”, version 5.0, from thecompany Olympus America Inc. Based thereupon the diameter based particlesize distribution and volume based particle size distribution areanalysed.

For a representative and reliable measurement of the micro-crystallinedomain size, the mean diameters of individual micro-crystallites, andthe analysis of the diameter based particle size distribution and volumebased particle size distribution, images from minimum three differentgranules should be analysed, for each granule a representative surfacearea should be selected, and the analysis per granules should compriseat least 75 individual particles on average. The results of thedifferent particles can be combined in one list to allow for thecalculation of a single overall particle size distribution.

In particular cases, the polycrystalline granules, or at least a largepart thereof, in particular the larger granules, have a globular shape.With the term “globular shape” is herein understood a shape with roundedoff edges without plane surfaces and crystallographic angles. Such shapecan be more or less spherical, or a shape like a patoto or a wallnut, oralike. Several granules, in particular the larger ones, also showcracks, as in dried mud. Smaller particles typically have a lessglobular shape and more pronounced cracks.

In other cases, the percentage of granules with a globular shape is muchless. In that case, even many of the bigger particles have a lessglobular shape and show very pronounced cracks. Also in these cases, allthe granules consist of multiple micro-crystallites having a particlesize much smaller than the granules.

The morphology with more globalur shapes is more observed with smallerdiamines whereas the morphology with the more pronounced cracking isobserved with larger diamines. Likewise this can be explained by amechanism involving swelling of the dicarboxylic acid particles uponabsorption and reaction with diamine, causing the particles to crack.This swelling, and thus the cracking will be more pronounced with largerdiamines.

Where the micro-crystallites have a small particle size, the granulestypically have a much larger particle size, even for the majority of thesmaller granules.

Suitably, the salt granulate material have a particle size distribution,with a d10 of at least 20 μm. Also suitably, the granulate material hasa particle size distribution with a a d90 of at most 1000 μm, andoptionally also median particle size (d50) in the range of 50-600 μm,Herein the particle size distribution is measured by the methodaccording to ISO 13320 as mentioned herein above.

In a preferred embodiment of the diamine/dicarboxylic acid salt the d10is in the range of 20-200 μm, and/or the d50 is in the range of 50-500μm, and/or d90 is in the range of 200-1000 μm. More particular, the d10of the diamine/dicarboxylic acid salt granules is in the range of 20-200μm, the d50 is in the range of 50-500 μm, and d90 is in the range of200-1000 μm.

Also preferably, the polycrystalline granules have a particle sizedistribution with a Span, defined by the ratio of (d84-d16)/d50, of atmost 5, preferably at most 2.5. The advantage is a more homogenousproduct, less fines and a better flowability.

A further characteristic of the diamine/dicarboxylic acid saltobtainable by the process according to the invention is that thegranulate material generally has a low compressibility. Thecompressibility is determined by the comparing the aerated bulk density(ABD) and the tapped bulk density (TBD). Suitably, the compressibility,expressed by the ratio of (TBD-ABD)/TBD*100%, is at most 35%, whereinABD is the aerated bulk density and TBD is the tapped bulk density bothmeasured by the method according to ASTM D6393.

The salt according to the invention is suitably comprises the salt ofone or of the dicarboxylic acids and one or more of the diamines, andany preferred combination thereof, as described herein further above.

Some examples include the following combinations: 6T/66; molar ratiosuitably in the range of 80/20-20/80, for example 62/38; PA 6T/610;molar ratio suitably in the range of 90/10-30/70, for example 70/30; PA6T/4T; molar ratio suitably in the range of 90/10-10/90, for example60/40; and PA 6T/10T; molar ratio suitably in the range of 90/10-30/70,for example 70/30. Herein is 4T the salt based on 1,4-butane diamine andterephthalic acid. 6T is the salt based on 1,6-hexane diamine andterephthalic acid. 66 is the salt based on 1,6-hexane diamine and adipicacid. 610 is the salt based on1,6-hexane diamine and adipic acid. 10T isthe salt based on 1,10-decane diamine and terephthalic acid.

More preferably, the salt comprises a salt based on 1,4-butane diamineand terephthalic acid and/or a salt based on 1,6-hexane diamine andterephthalic acid. More particular the is based on 1,4-butane diamineand terephthalic acid with terephthalic present in an amount of at least70 mol % of total diacid and 1,4-butane diamine present in an amount ofat least 10 mol % of total diamines. Even more preferably, the salt isan anhydrous 4T or 6T salt.

The invention also relates to the use of the salts in a polymerizationprocess for the preparation of a polyamide.

The invention is further illustrated with the following examples andcomparative experiments.

Methods

Melting Temperature.

The melting temperature (Tm) was measured by DSC according to the methodof ISO11357-3.2, 2009, in an N2 atmosphere with heating and coolingrates of 20° C./min. Herein Tm was the temperature measured for the peakvalue of the melting peak in the first heating cycle.

Aerated Bulk Density (ABD) and Tagged Bulk Density (TBD)

The ABD and TBD were measured by the method according to ASTM D6393-08(“Standard Test Method for Bulk Solids Characterization by CarrIndices”, ASTM International, West Conshocken, Pa., DOI:10.1520/D6393-08) with a Hosokawa Powder Tester at 20° C.

Particle Size Distribution

The particle size distribution of granulate material was measured bylaser granulometry according to ISO 13320-1 with a Sympatec Helos(H0024) & Rodos apparatus at 20° C. with an applied pressure of 0.5 barand an measured under-pressure in the venturi of 25 mbar.

Shear Test

The flowability was measured by the method according to ASTM StandardD6773-08 (“Standard Shear Test Method for Bulk Solids Using the SchulzeRing Shear Tester”, ASTM International, West Conshocken, Pa., DOI:10.1520/D6773-08). The shear test was performed with a Schulze RingshearTester at 20° C. with a consolidation stress of 3 kPa. The measurementwas started immediately after filling of the tester.

Porosimetry

The porosity was measured by the method of Mercury Intrusion Porosimetry(MIP) experiments carried out on a Micromeritics Autopore IV 9505porosimeter (www.micromeritics.com) in the pressure range from vacuum upto 22 MPa. Prior to the measurements, the samples were kept in vacuumfor 16 h. The samples, about 0.15 g of dried material each, were thentransferred and weighed in the sample holder.

Micro-Crystalline Domain Size

The size of the micro-crystalline domains was analysed with the help ofthe image analysis software program “Analysis.auto”, version 5.0, fromthe company Olympus America Inc. For the analysis, SEM images taken fromsurface areas of different granules were used. Depending on the surfacearea of the granules covered by the image and the size of themicro-cystallites, selections of parts of the images were used.

In a typical example, the original image had a size corresponding with asurface area of 15×20 μm. The image had 3872×3306 pixels. From the imagea representative part corresponding with a surface area of about 5×6 μmwas selected. The image had 1238×963 pixels.

After selection of an appropriate part, the “Operation” procedureprovided in the software program was performed as follows: first ashading correction was applied using N×N average filter with 6iterations and size selection 6, as provided by the software. Then, theimage is converted to a negative image. From the converted image arepresentative part was selected.

In the typical example the selection was about 3.4×4.0 μm (3.39×3.94μm).

The selection was transformed into a binary image while applying a lowvalue (equal or close to 0) for the low threshold and a high value(around 210) for the high thresholds for the detection set. In thebinary image, contours are applied and corrected with the “edit image”option in the software to remove artefacts. This edited image is usedfor the “Particle analysis” procedure.

In this analysis, particles with a size of at least 10 pixels aredetected. The detected particles are then analysed for the surface area,the smallest- and largest diameter and mean diameter. The resulting dataare transferred to Excel.

For the further analysis as used herein the data for the mean diametersof the individual particles was used. Based on the values of the meandiameter of the individual particles a theoretical volume for each ofthe particles was calculated, assuming the particles being ideallyspherical. Based thereupon, and combing the results of 3 differentparticles, a volume based particle size distribution was calculated andthe d10, d50 and d90 values calculated.

Starting Materials

-   Terephthalic acid Industrial grade (BP Amoco); 0.05 wt. % water-   Adipic acid Industrial grade (Rhodia); 0.09 wt. % water-   Sebacic acid Industrial grade (Sigma Aldrich)); <0.1 wt. % water-   1,4-butane diamine Industrial grade (DSM); <0.5 wt. % water-   1,6-hexane diamine Industrial grade (Sigma Aldrich); <0.5 wt. %    water-   1,10-decane diamine Industrial grade (Sigma Aldrich); <0.5 wt. %    water    In performing g to mol conversion, chemicals are seen as 100% pure.

SALT PREPARATION EXPERIMENTS Example I

A mixture of 75 g of terephthalic acid and 40.4 g of adipic acid (62/38mol %) was charged into a 1.0 liter baffled flask, attached to a rotaryevaporator, equipped with a heated diamine dosing vessel was kept underan inert nitrogen atmosphere and mixed by rotation at 50 rpm. Therotating flask was partially submerged in a water bath, maintained at60° C. to remove the heat of neutralization. Liquid 1,6-hexane diamine(86.6, i.e. around 2 molar % in excess of stoichiometric quantity, orD/DA=1.02) of 60° C. was added drop-wise to the acids in 4 hours underconstant rotation. After dosing, the reaction mixture was stirred byrotation at a water batch temperature of 60° C. for another 20 minutes.After the experiment, salt in the form of loose powder, was obtained.

In similar manners as above, the compositions of Examples II-VI andlisted in table 1 were prepared.

Example II

Example II was prepared as described in example I, starting from a mixof 79.3 g terephthalic acid and 41.4 g of sebacic acid (70/30 mol %) andadding 81.3 g of liquid 1,6-hexane diamine in 4 hours, resulting in aloose powder with D/DA=1.026

Example III

Example III was prepared as described in example I, starting from 122.5g terephthalic acid and adding a liquid mix of 52.8 g 1,6-hexane diamineand 28.7 g 1,4-butane diamine (60/40 mol % excluding the 2.7 g1,4-butane diamine excess) in 2 hours, resulting in a loose powder withD/DA=1.026.

Example IV

Example IV was prepared as described in example I, starting from 111.1 gterephthalic acid and adding a liquid mix of 56.4 g 1,6-hexane diamineand 34.6 g 1,10-decane diamine (62/38 mol % excluding the 2.0 g1,6-hexane diamine excess) in 4 hours, resulting in a loose powder withD/DA=1.026.

Example V

Example V was prepared as described in example I, starting from 111.1 gterephthalic acid and adding 84.3 g liquid 1,6-hexane diamine in 5hours, resulting in a loose powder with D/DA=1.024.

Example VI

Example VI was prepared as described in example I, using a 2 literbaffled flask starting from 326.65 g terephthalic acid and adding 178.35g liquid 1,4-butane diamine in 3 hours, resulting in a loose powder withD/DA=1.029.

Comparative Experiment A: 4T Salt Preparation in Water Via an AqueousSolution Process

A 2000 ml three necked flask, equipped with a reflux condenser, atemperature sensor and a magnetic stirring rod was charged with 300 gdemineralized water and 104.01 g DAB. Over 1 minute 195.99 gterephthalic acid (TPA) is added via a funnel attached to the thirdneck. In course of the TPA addition, the 4T salt forms as a whiteslurry. 600 g water was added and subsequently, the reaction mixture washeated to T=90° C. at which temperature the 4T salt was dissolved. Theproduct was then cooled in a water/ice bath and the cooled slurry wasfiltered over a Büchner funnel. The mother liquor was mixed with 800 mlethanol and the precipitated salt collected on the same Büchner funnel.The filter cake was washed with 200 ml ethanol. After air drying, byallowing a stream of air to pass through the filter cake for 16 hours,the product was mixed to homogenize the two precipitation fractions anddried under vacuum (50 mbar abs Pressure) at 40° C. for by for 3 hours.The product had a melting point of 283° C., determined by DSC.

TABLE 1 Salt preparation results, laboratory scale Salt CompositionMolar ratio Observations Tm (° C.) Example I 6T/66 62/38 powder obtained199, 275 Example II 6T/610 70/30 powder obtained 180, 277 Example III6T/4T 60/40 powder obtained 280 Example IV 6T/10T 70/30 powder obtained254, 264 Example V 6T powder obtained 280 Example VI 4T powder obtained283 Comp. Ex. A 4T Powder 283 a) In case of using more than twodiamines, for calculating the molar composition of the copolyamides, thediamine excess was accounted to the lowest molar mass diamine in thediamine mix and was not included for the molar ratio compositioncalculation.

Table 2 shows an overview of properties measured for 4T salt of ExampleVI and 4T salt of Comparative experiment A (CE-A). Microscopic picturesof these materials are shown in the attached figures.

TABLE 2 Properties of 4T salt of Example VI and 4T salt of Comparativeexperiment A EX-VI CE-A Particle Size Distribution d10 (μm) 45 4.6 d50(μm) 143 42 d90 (μm) 292 503 d16 (μm) 60 7.0 d84 (μm) 253 370 d99 (μm)441 796 Span ((d84 − d16)/d50) 1.35 8.33 Sheartest Sigma 1 [Pa] 57316103 FC [Pa] 4 1878 FFC [—] 1500 3 Phie [°] 37 40 Aerated Bulk Density(ABD) and Tapped Bulk Density (TBD) ABD [kg/m3] 523 360 TBD [kg/m3] 675625 Compressibility (1 − (ABD/TBD)) 0.225 0.424 Mercury Porosimetry Peak(μm) 70 10 Peak hight (dV/dlogD) (cm³/g) 2.25 1.3 Above 100 μm LittleSignificant Porosity (%) 53 59

The results not only show differences in particle size distribution andflow behaviour, but also in the crystalline morphology. EX-VI shows anarrow particle size distribution with a relatively high d10 and lowspan, and a low compressibility, whereas CE-A shows a broader particlesize distribution with a lower d10 and higher span, and a highercompressibility. The difference in particle size distribution andcompressibility is also reflected in the porosity measurements. Most ofthe porosity is found in “pores” with a pore size in the range of 5-500μm (EX-VI), respectively 2-600 μm (CE-A), likewise corresponding withthe inter-particle porosity. EX-VI has a peak at larger pore size (70μm), which is higher and more narrow (running from 20-100 μm) than thatof CE-A. CE-A has a lower, but much broader pore size distribution, withthe peak at much lower pore size (10 μm), but still with a significantamount of pores with a size above 100 μm.

The different crystalline morphologies are further illustrated with theSEM-images shown in FIGS. 1-5.

FIG. 1: SEM image of 4T salt from Comparative Example A.

FIG. 2-5: SEM images of 4T salt from Example VI.

FIG. 1 shows a SEM image taken of 4T salt from Comparative Example A.The image shows large irregular shaped granules composed of multiplesmaller crystals with relative large size, respectively composed of alimited number of crystals with a even larger size and rather flatsurface areas. Next to that these larger granules, there are visible alarge number of small granule, several consisting of a single crystal oronly a few crystals. Many of these crystals are still in the size rangearound 5-10 μm.

FIG. 2 shows an SEM image taken of 4T salt from Example VI. The imageshows a large number of granules with a globular shape. The smallerparticles have a less globular shape. The number of small particles isrelatively low.

FIG. 3 shows an SEM image taken from a selected area of the SEM image ofFIG. 2, highlighting a granule with a globular shape. In the granuleeffects of cracking, like in dried mud, are visible.

FIG. 4 shows an SEM image taken from a selected area of the SEM image ofFIG. 3, highlighting the surface area of the globular granule. On thesurface of the granule, many small crystallites are visible.

FIG. 5 shows an SEM image taken from another selected area of the SEMimage of FIG. 2, highlighting a part of a granule with a globular shapeand a smaller granule with a more irregular shape. The latter granuleshows even more severe effects of cracking, like in dried mud, comparedto the globular granule of FIG. 3.

Micro-Crystalline Domain Size of Example VI

For the salt of Example VI the particle size distribution of themicro-crystalline domains was determined both on the surface on theparticles, and inside the particles. For the latter cross-cut particleswere used. FIGS. 6-14 illustrate the different steps in the analyticalprocedure, starting with a SEM image of the inside of a salt granule(FIG. 6), respectively with a SEM image of the inside of a salt granule(FIG. 10), of example VI. Results are presented in table 3.

FIG. 6-9: Images of microcrystalline domains inside a 4T granule,following different steps in the particle size analysis.

FIG. 10-13: Images of microcrystalline domains on the outside of a 4Tgranule, following different steps in the particle size analysis.

FIG. 6 shows the original SEM image of the 4T salt of example VI,showing the microcrystalline domains inside a granule.

FIG. 7 shows a selection of FIG. 6, wherein the image has been optimizedin contrast and shading correction has been applied.

FIG. 8 shows a selection of FIG. 7, wherein the image has been invertedand further optimized in contrast.

FIG. 9 shows a selection of FIG. 8, wherein the image has beenbinarized, edited and made ready for the particle size analysis.

FIG. 10 shows a SEM image of the 4T salt of example VI, showing themicrocrystalline domains on the outside of a granule. The SEM image isalready optimized in contrast and shading correction has been applied.

FIG. 11 shows a selection of FIG. 10, wherein the image has beeninverted and further optimized in contrast.

FIG. 12 shows a the same selection as of FIG. 8, wherein the image hasbeen binarized.

FIG. 13 shows a selection of FIG. 12, wherein the image has been editedand made ready for the particle size analysis.

TABLE 3 Results of the micro-crystalline domain size analysis of ExampleVI Particle size Inside Outside D10-volume based (nm) 469 1080D50-volume based (nm) 724 1880 D90-volume based (nm) 1050 2350 Smallest(nm) 12 140 Largest (nm) 1128 2700 D50-diameter based (nm) Around 300Around 1100

Examples VII and VIII

Examples VII and VIII were repetitions of Example VI, except that theterephthalic acid used was different. For Example VII a special gradewith a narrow particle size distribution and a small median particlesize was used. For Example VIII a special grade also with a narrowparticle size distribution but with a larger median particle size wasused. In both cases a free flowing powder was obtained. The results forthe particle size distribution for the specific grades of terephthalicacid (referred to as Comparative experiment B and C) and Example VII andExample VIII and the flowability of 4T salt of Example VII and ExampleVIII are shown in Table 4.

TABLE 4 Properties of 4T salt of Example VII and Example VIII andterephthalic acid of Comparative Experiment B and C. CE- EX-VII CE-EX-VIII TPA 4T TPA 4T Particle Size Distribution D10 30 44 110 100 D5081 107 200 240 d90 141 177 321 365 d16 39 56 133 155 d84 126 163 288 338d99 196 263 490 502 Span ((d84 − d16)/d50) 1.07 1.00 0.78 0.76 SheartestSigma 1 [Pa] 5848 6152 FC [Pa] 304 528 FFC [—] 19 12 Phie [°] 37 39Aerated Bulk Density (ABD) and Tapped Bulk Density (TBD) ABD [kg/m3] 846548 884 489 TBD [kg/m3] 1064 678 1026 594 Compressibility 0.205 0.1910.139 0.177 (1 − (ABD/TBD))

The results show that particle size distribution of the terephthalicacid starting material is directly reflected in the particle sizedistribution, apart from the fact that the dimensions, or at least mostof them, have gone up systematically. This increase in particle size, incombination with retention of the particle size distribution, might beexplained absorption and reaction of the diamine with the dicarboxylicacid, thereby expanding the dicarboxylic acid particles without breakingthem up. At the same time the density has gone down significantly, mostfor EX VIII, but the compressibility is still very low. The lowerdensity may be due to lower intrinsic density of the salt compared tothe acid as well as due to small cracks in the particles and smallspacing between micro-crystallites. The results of the shear test showthat both materials are free flowing.

Example IX

Mixtures of adipic acid (ranging from 25 to 100 kg per batch) andterephthalic acid (ranging from 350 to 425 kg per batch) were chargedinto a 3000 liter tumble dryer. After inertization with nitrogen, amixture of molten (100%, industrial grade) 1,4-butane diamine (25-100kg) and 1,6-hexane diamine (200-275 kg) of 50° C. was sprayed onto thesolid acids at atmospheric pressure, through a perforated platedistributer, in approx. 4 hours, while tumbling the complete dryer mass.The product temperature was measured in time using a PT-100 elementinside the dryer and the dryer content was maintained below 80° C. bycooling via the dryer walls. After dosing and mixing for another hour,the salt obtained had the appearance of a free-flowing, crystalline,white powder.

Example X

Mixtures of adipic acid (ranging from 2.5 to 10 kg per batch) andterephthalic acid (ranging from 35 to 42.5 kg per batch) were chargedinto a 180 liter conical dryer with a helical stirrer. Afterinertization with nitrogen, first (100%, industrial grade) 1,4-butanediamine (2.5-10 kg), then (100%, industrial grade) 1,6-hexane diamine(20-27.5 kg) were sprayed onto the solid acids at atmospheric pressure,through a 4 pipe (Swazeloc ⅛″) distributer, in approx. 1.5 to 2 hours,while agitating the reaction mass with the helical stirrer. The producttemperature was measured in time using a PT-100 element flush with thedryer wall and the dryer content was maintained below 65° C. by coolingvia the dryer walls. After dosing, heating to 150° C. under nitrogen andsubsequent cooling, the salt obtained had the appearance of afree-flowing, crystalline, white powder. The same procedure was repeatedseveral times using pre-mixed amine mixtures of 1,4-butane diamine(2.5-10 kg) and (100%, industrial grade) 1,6-hexane diamine (20-27.5kg), leading to very similar, free-flowing, crystalline, white powders.

Example XI

Terephthalic acid (45 kg) was charged into a 180 liter conical dryerwith a helical stirrer. After inertization with nitrogen, a mixture of(100%, industrial grade) 1,4-butane diamine (2.5-10 kg) and (100%,industrial grade) 1,6-hexane diamine (20-27.5 kg) was sprayed onto thesolid acid at atmospheric pressure, through a 4 pipe (Swazeloc ⅛″)distributer, in approx. 1.5 to 2 hours, while agitating the reactionmass with the helical stirrer. The product temperature was measured intime using a PT-100 element flush with the dryer wall and the dryercontent was maintained below 65° C. by cooling via the dryer wall. Afterdosing, and mixing for another hour, the salt obtained had theappearance of a free-flowing, crystalline, white powder.

Example XII

Mixtures of adipic acid (ranging from 0.6 to 2.7 kg per batch) andterephthalic acid (ranging from 9.3-11.3 kg per batch) were charged intoa 50 liter DRAIS ploughshare mixer. After inertization with nitrogen, amixture of (100%, industrial grade) 1,4-butane diamine (0.6-2.7 kg) and(100%, industrial grade) 1,6-hexane diamine (5.4-7.4 kg) was sprayedonto the solid acids at atmospheric pressure, through a single (Swazeloc⅛″) pipe, in around 1 hour, while agitating the reaction mass with theploughshare mixer. The product temperature was measured in time using aPT-100 element inserted into the dryer in between the plough-shares, andthe dryer content was maintained below 70° C. by cooling via the mixer.After dosing and mixing for another hour, the salt obtained had theappearance of a free-flowing, crystalline, white powder.

Example XIII

Mixtures of adipic acid (ranging from 0.8 to 3.3 kg per batch),terephthalic acid (ranging from 11.6 to 14.2 kg per batch) and benzoicacid (ranging from 0.1 to 0.6 kg per batch) were charged into a 100liter tumble dryer. After inertization with nitrogen, a mixture ofmolten (100%, industrial grade) 1,4-butane diamine (0.8-3.3 kg) and1,6-hexane diamine (6.6-9.2 kg), at a temperature of 50° C., was sprayedonto the solid acids at atmospheric pressure, through a 4 fold (Swazeloc⅛″) pipe distributer, in approx. 2 hours, while tumbling the completedryer mass. The product temperature was measured in time using a PT-100element inside the dryer and the dryer content was maintained below 80°C. by cooling via the dryer walls. After dosing and mixing for anotherhour, the salt obtained had the appearance of a free-flowing,crystalline, white powder.

The invention claimed is:
 1. A process for preparing adiamine/dicarboxylic acid salt comprising the steps of: (i) forming areaction mixture by contacting a diamine liquid with a dicarboxylic acidpowder comprising an aromatic dicarboxylic acid, wherein thedicarboxylic acid powder has a particle size distribution with a Span,defined by a ratio of (d84−d16)/d50, of at most 5; and (ii) allowing thediamine and the aromatic dicarboxylic acid in the reaction mixture toreact to form a diamine/dicarboxylic acid salt, wherein step (i)comprises the steps of: (a) gradually dosing the diamine liquid to thearomatic dicarboxylic acid powder, while keeping the aromaticdicarboxylic acid powder in constant movement, and thereafter (b)keeping the reaction mixture in constant movement for a time perioddirectly following completion of the dosing; wherein steps of (a) and(b) are carried out at a temperature above 0° C. and below all of thefollowing: the boiling temperature of the diamine and the meltingtemperatures of the dicarboxylic acid, the diamine/dicarboxylic acidsalt and any intermediate reaction product, and wherein the reactionmixture in steps (a) and (b) comprises at most 5 wt. % of water,relative to the total weight of the diamine and dicarboxylic acid; andwherein the diamine consists of a mixture of different diamines.
 2. Theprocess according to claim 1, wherein the diamine and the dicarboxylicacid in the reaction mixture are present in a molar ratio of diamineover dicarboxylic acid in the range of 0.9-1.1.
 3. The process accordingto claim 1, wherein the dicarboxylic acid powder is a mixture of analiphatic dicarboxylic acid and an aromatic dicarboxylic acid.
 4. Theprocess according to claim 3, wherein the mixture of aliphaticdicarboxylic acid and aromatic dicarboxylic acid is a dry blend of solidparticles of the aliphatic dicarboxylic acid and solid particles of thearomatic dicarboxylic acid.
 5. The process according to claim 3, whereinthe aliphatic dicarboxylic acid and the aromatic dicarboxylic acid arepresent in a molar ratio between 90:10 and 10:90.
 6. The processaccording to claim 1, wherein the dicarboxylic acid consists of 90-100mole % of aromatic dicarboxylic acid and 10-0 mole % of aliphaticdicarboxylic acid.
 7. The process according to claim 1, wherein thearomatic dicarboxylic acid comprises either isophthalic acid,terephthalic acid or naphthalene dicarboxylic acid, or any combinationthereof.
 8. The process according to claim 1, wherein the aliphaticdicarboxylic acid comprises adipic acid and/or sebacic acid.
 9. Theprocess according to claim 1, wherein the diamine comprises an aliphaticdiamine having 4-12 carbon atoms.
 10. The process according to claim 9,wherein the diamine comprises 1,4-butane diamine and/or 1,6-hexanediamine.
 11. The process according to claim 1, wherein step (i)comprises contacting the diamine liquid and the dicarboxylic acid powderby spraying or dripping the diamine liquid onto dicarboxylic acid powderwhile moving the dicarboxylic acid powder.
 12. The process according toclaim 1, wherein step (i) comprises contacting and mixing the diamineliquid and the dicarboxylic acid powder in a tumble mixer, a ploughsharemixer, a conical mixer, a planetary screw mixer or a fluidized bedreactor.
 13. The process according to claim 1, wherein step (i)comprises contacting the diamine liquid and the dicarboxylic acid powderat a temperature between 0° C. and the boiling temperature of water. 14.The process according to claim 1, which further comprises the step of(iii) removing neutralization heat produced upon reaction of the diamineand the dicarboxylic acid to form the diamine/dicarboxylic acid salt viaa heat exchanger.
 15. A diamine/dicarboxylic acid salt, derived fromdicarboxylic acid comprising an aromatic dicarboxylic acid and diaminecomprising of a mixture of different aliphatic diamines, wherein thesalt is a granulate material obtained by the process according toclaim
 1. 16. The salt according to claim 15, wherein the salt is ananhydrous salt, comprising less than 0.5 wt. % water, relative to thetotal weight of the salt.
 17. The salt according to claim 15, whereinthe salt has a flowability defined by the ratio (ffc) of consolidationstress, σ1, to unconfined yield strength, ac, measured by the shear testmethod according to ASTM D6773 of at least
 10. 18. The salt according toclaim 15, wherein the salt is a granulate material consisting ofpolycrystalline granules comprising micro-crystallites, wherein themicro-crystallites have a particle size distribution, measured bysoftware supported analysis of SEM images taken from surface areas ofgranules, with a volume based d90 of at most 5 μm.
 19. The saltaccording to claim 15, wherein the salt is a granulate materialconsisting of polycrystalline granules, wherein the polycrystallinegranules have a particle size distribution, measured by the methodaccording to ISO 13320, with a d10 of at least 20 μm, a d90 of at most1000 μm, and a median particle size (d50) in the range of 50-600 μm. 20.The salt according to claim 19, wherein the dl 0 is in the range of20-200 μm, the d50 is in the range of 50-500 μm, and the d90 is in therange of 200-1000 μm.
 21. The salt according to claim 15, wherein thepolycrystalline granules have a particle size distribution with a Span,defined by the ratio of (d84−d16)/d50, of at most
 5. 22. The saltaccording to claim 15, wherein the granulate material has acompressibility, expressed by the ratio of (TBD−ABD)/TBD*100%, of atmost 35%, wherein ABD is an aerated bulk density and TBD is a tappedbulk density both measured by the method according to ASTM D6393. 23.The salt according to claim 15, wherein the salt comprises a salt basedon 1,4-butane diamine and terephthalic acid and/or a salt based on1,6-hexane diamine and terephthalic acid.
 24. The salt according toclaim 21, wherein the Span of the polycrystalline granules is at most2.5.
 25. A process for the preparation of a polyamide which comprisesforming a polyamide using the salt according to claim 15.